On Mon, Feb 18, 2013 at 8:39 PM, Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx> wrote: > @@ -200,6 +217,16 @@ void percpu_write_lock_irqsave(struct percpu_rwlock *pcpu_rwlock, > > smp_mb(); /* Complete the wait-for-readers, before taking the lock */ > write_lock_irqsave(&pcpu_rwlock->global_rwlock, *flags); > + > + /* > + * It is desirable to allow the writer to acquire the percpu-rwlock > + * for read (if necessary), without deadlocking or getting complaints > + * from lockdep. To achieve that, just increment the reader_refcnt of > + * this CPU - that way, any attempt by the writer to acquire the > + * percpu-rwlock for read, will get treated as a case of nested percpu > + * reader, which is safe, from a locking perspective. > + */ > + this_cpu_inc(pcpu_rwlock->rw_state->reader_refcnt); I find this quite disgusting, but once again this may be because I don't like unfair recursive rwlocks. In my opinion, the alternative of explicitly not taking the read lock when one already has the write lock sounds *much* nicer. -- Michel "Walken" Lespinasse A program is never fully debugged until the last user dies. -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
